A JAR with an embedded server is fully self-contained and runs standalone via `java -jar` — the standard, recommended approach for Spring Boot apps, especially in containerized deployments. A WAR is built for deployment into an external, pre-existing servlet container (like a standalone Tomcat installation) — supported by extending `SpringBootServletInitializer`, but mainly relevant for organizations with existing infrastructure requiring deployment into a shared, externally managed application server rather than each app bringing its own embedded one.

Intermediate5 min

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#JAR#WAR#Packaging

What is the difference between packaging a Spring Boot app as a JAR versus a WAR?

WAR Deployment Mostly Persists for Legacy/Compliance Reasons Now

In a modern containerized deployment (Docker/Kubernetes), there's little practical reason to deploy a WAR into a shared external Tomcat rather than just running the self-contained jar in its own container — WAR packaging today mostly persists in organizations with existing shared application-server infrastructure and operational processes built around it, not because it offers any technical advantage for a new Spring Boot application.